Elastin is the extracellular matrix protein that imparts the property of elasticity to the lung and blood vessels. Its importance to both tissues is absolute. Without elastin the organism does not survive. With abnormal elastin, tissue development and function are compromised. The component of arteries and the lung in higher vertebrates that accounts for their elastic properties is the elastic fiber network. Ultrastructural analysis of elastic fibers identified two components: the protein elastin and fibrillin-containing microfibrils. Understanding how elastic fibers are formed, however, has been difficult. During the past funding period we showed that elastic fiber assembly is more complicated and the players more numerous than previously thought. Thus, the overall objective of this renewal application is to better understand the assembly pathway and investigate the expanding list of molecules that participate in the process. The experimental approach will utilize in vitro assembly models supported by live cell imaging to identify the proteins involved in elastin assembly. We will also utilize quick-freeze, deep-etch electron microscopy to characterize elastic fiber assembly at the tissue level. Finally, we will build upon results obtained during the previous funding period to better understand the molecular organization of fibrillin-containing microfibrils. Our specific aims are: 1) Identify the spatial and temporal appearance and functional interactions of key assembly proteins during the early stages of elastic fiber formation. 2) Investigate the underlying mechanisms of autosomal dominant cutis laxa (ADCL) and the possibility that elastin assembly occurs through different mechanisms in different tissues. 3) Characterize elastic fiber assembly and matrix ultrastructure in intact tissues using DEEM. 4) Elucidate the molecular structure of fibrillin-containing microfibrils.